Single wafer type substrate cleaning method and apparatus

ABSTRACT

In the drying step of the single wafer type substrate cleaning system for cleaning wafers not stored in a cassette, in a sealed cleaning housing, a spin drying treatment is applied to the wafer when the wafer is supported and rotated at high speed while an inert gas for preventing oxidation is supplied to the face of the wafer, and the amount of the inert gas to be supplied to the face of the wafer is larger at the outer peripheral portion of the wafer than that supplied at the center thereof, thereby preventing oxidation on the face of the wafer effectively while optimizing the benefits of the single wafer type cleaning system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a single wafer type substrate cleaning methodand a single wafer type substrate cleaning apparatus, more particularlyto a single wafer type wet cleaning technique or system for applying acleaning treatment to substrates such as semiconductor wafers one by oneduring the fabrication process as well as certain devices such aselectronic parts and the like.

2. Prior Art

A so-called batch type wet cleaning system has been the principal methodof cleaning substrates such as semiconductor wafers (hereinafterreferred to simply as “Wafers”), whereby wafers stored in a carriercassette are immersed in sequence in wet bench type cleaning bathsarranged in series, or wafers are directly immersed in the cleaningbaths through a transfer unit without being stored in a carriercassette. However, semiconductor devices have reached the sub micronage, in that they are now micro-fabricated and highly integrated, suchthat the face of wafers has recently required a very high degree ofcleaning density, and wafers which are not stored in a cassette have tobe wet-cleaned individually in a sealed cleaning housing. To this end, aso-called single wafer type wet cleaning system intended to meet therequirement of a higher cleaning density has been developed.

Under the single wafer type wet cleaning system, wafers can be cleanedwith the use of a simple and compact cleaning system in a relativelyclean atmosphere where particles and the like do not settle or remain onthe face of the wafer. This system is therefore practical to use forsmall scale production.

Under the single wafer type cleaning system, wafers can be cleaned bythe application of various chemical fluids on the face of wafers in apredetermined order, and finally dried by a spin drying treatmentwhereby the wafers are rotated at high speed. However, there are caseswhere oxygen remains in the sealed cleaning housing during the dryingtreatment phase depending on the kind of chemical fluid used, such thatthe face of a wafer is prone to oxidization. Accordingly, improvement ofthe system is desirable.

SUMMARY OF THE INVENTION

The present invention has been made in view of the aforementionedconventional problems, and it is the object of the invention to providea single wafer type cleaning method capable of effectively preventingthe face of the wafer from becoming oxidized while optimizing thebenefits of the single wafer type wet cleaning system for individuallycleaning wafers which are not stored in a cassette in a sealed cleaninghousing.

Another object of the invention is to provide a single wafer typecleaning apparatus having the means of carrying out the single wafertype cleaning method set forth above as the first object of theinvention.

To achieve these objectives, the proposed method comprises theapplication of a spin drying treatment to the wafer when the wafer issupported and rotated at high speed while an inert gas for preventingoxidation is supplied to the face of the wafer during the dryingprocess, and the inert gas supplied to the face of the wafer is suchthat the amount supplied at the outer region of the wafer is larger thanthat supplied at the center thereof.

In the preferred embodiment, a sealed drying space is intended to beformed at the outer region of the face of the wafer and inert gas issupplied to the inside of the sealed drying space, wherein the inert gasis a nitrogen gas (hereinafter referred to as “N₂ gas”).

Further, the single wafer type cleaning apparatus of the invention whichis deemed suitable for carrying out the foregoing cleaning methodcomprises (1) a wafer rotary means for supporting and rotating a singlewafer in a horizontal position in the cleaning housing; (2) a cleaningchamber provided at the outer region of the wafer rotary means for thepurpose of forming a cleaning treatment space for the wafer which isrotatably supported by the wafer rotary means; (3) a chemical fluidsupply means for supplying cleaning fluid to the face of the wafer whichis rotatably supported by the wafer rotary means; (4) and an inert gassupply means for supplying N₂ gas intended to prevent oxidation on theface of the wafer which is rotatably supported by the wafer rotarymeans, wherein the supply port of the inert gas supply means is designedin such a manner that the amount of N₂ gas supplied to the outer regionof the face of the wafer is larger than that at the center thereof.

In the preferred embodiment, the inert gas supply means has a gasinjection section consisting of a circular cover body intended to form asealed drying space at the outer region of the face of the wafer whichis rotatably supported by the wafer rotary means while cooperating withthe cleaning chamber, wherein the gas injection section comprises a flathollow body which communicates with an inert gas supply source at theinside thereof and the supply port at the plane bottom portion.

The supply port of the gas injection section comprises a plurality ofinjection openings which are disposed radially and arrangedconcentrically with the face of the wafer, which is rotatably supportedby the wafer rotary means, and these injection openings are designed insuch a manner that the sum of the areas of the injection openings at theouter region of the face of the wafer is larger than that at the centerthereof as the injection openings direct toward the outer region of thewafer.

Further, a baffle plate is interposed in the hollow section of the gasinjection section to prevent the inert gas from directly flowing to thecenter of the supply port of the inert gas.

Under the single wafer type cleaning system of the invention, the faceof the wafer is cleaned by employing various chemical fluids in thesealed cleaning housing in a predetermined order, and finally the waferis dried through a spin drying treatment while the wafer is rotated athigh speed, in which case, oxygen will likely remain in the sealedcleaning chamber during the drying process depending on the kind ofchemical fluid(s) used, resulting in oxidation on the face of the wafer.

To address the foregoing problem, the invention proposes to provide aspin drying treatment to the wafer which is supported and rotated by thewafer rotary means at high speed while being supplied with N₂ gas forpreventing oxidation on the face of the wafer.

The degree of oxidation on the wafer depends on the concentration ofoxygen in the circum-ambient atmosphere on the face of the wafer, and ithas been found, as a result of research and tests conducted by theinventors, that concentration of oxygen in the circum-ambient atmosphereon the face of the wafer is higher at the outer peripheral portion ofthe face of the wafer than that at the center thereof in an ordinarystate.

It is thus necessary to make the concentration of oxygen at the outerperipheral portion of the face of the wafer to become zero (0) or closeto zero (0) so as to prevent oxidation on the wafer, and to achievethis, the cleaning housing should be purged by supplying N₂ gas to theinside thereof. This however requires a considerable volume of N₂ gaswhich would increase running costs and is therefore uneconomical.

According to the invention, the amount of N₂ gas to be supplied to theface of the wafer must be such that the amount supplied to the outerperipheral portion of the wafer is larger than that at the centerthereof so that concentration of oxygen is allowed to become zero (0) orclose to zero (0) while reducing the usage of N₂ gas as much as possiblein order to prevent oxidation on the face of the wafer.

Described more in detail, the drying process of the single wafer typecleaning system for individually cleaning wafers which are not stored ina cassette in the sealed cleaning housing, entails the support androtation of the wafer at high speed by the wafer rotary means, therebyapplying a spin drying treatment to the wafer while N₂ gas forpreventing oxidation is supplied to the face of the wafer, and theamount of inert gas supplied to the face of the wafer is such that theamount of inert gas supplied to the outer peripheral portion of thewafer is larger than that at the center thereof. Accordingly, it ispossible to improve and enhance the usefulness of the single wafer typecleaning system by providing a method of effectively preventingoxidation on the face of the wafer.

That is, under the single wafer type cleaning system, the wafer iscleaned by the introduction of various chemical fluids in the sealedcleaning housing in a predetermined order, and finally dried through aspin drying treatment while the wafer is rotated at high speed, andsimultaneously supplying an N₂ gas for preventing oxidation on thewafer. The degree of oxidation that develops on the wafer depends on theconcentration of oxygen in the circum-ambient atmosphere on the face ofthe wafer.

According to the invention therefore, if the amount of N₂ gas suppliedto the face of the wafer is such that the amount of N₂ gas supplied tothe outer peripheral portion of the wafer is larger than that at thecenter thereof, the concentration of oxygen is substantially reduced tozero (0) or close to zero (0) while the usage of N₂ gas is decreased asmuch as possible, thereby preventing oxidation on the face of the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front sectional view showing the internal construction of asingle wafer type cleaning apparatus according to the preferredembodiment of the invention;

FIG. 2 is an enlarged sectional front view showing the locationalrelationship between the wafer rotary section and the inert gas supplysection of the single wafer type cleaning apparatus;

FIG. 3 is an enlarged sectional front view showing the locationalrelationship between the wafer rotary section and the inert gas supplysection in the drying step;

FIGS. 4(A) to (C) are bottom views respectively showing concreteconstructions of the injection openings of the gas injection section inthe inert gas supply section; and

FIG. 5 is a view showing the distribution of the concentration of oxygenin the circum-ambient atmosphere on the face of a wafer which issupported by a wafer supporting section of the wafer rotary section inan ordinary state.

PREFERRED EMBODIMENT OF THE INVENTION

The preferred embodiment of the invention is described with reference tothe attached drawings.

A single wafer type cleaning apparatus is illustrated in FIG. 1, whereineach wafer W, which is not stored in a cassette, is wet-cleanedindividually in a sealed cleaning housing 1, and the sealable cleaninghousing 1 comprises a wafer rotary section (wafer rotary means) 2 forrotatably supporting one wafer W in the horizontal position, a cleaningchamber 3 which is relatively vertically movable, a chemical fluidsupply section (chemical fluid supply means) 4 for supplying thecleaning fluid, an inert gas supply section (inert gas supply means) 5for supplying the N₂ gas for oxidation prevention, and a controller 6for controlling these driving sections while interlocking mutuallytherewith as major components.

The cleaning housing 1 is sealable at the upper portion for the cleaningtreatment and serves as a location for installing various unit drivingsections at the lower portion disposed in the upper space. A closablewafer taking in-out port, not shown in detail, through which the wafer Wis taken in or taken out in the upper space of the cleaning housing 1,is structured in such a way to secure airtightness and watertightnesswhen it is closed.

The wafer rotary section 2 horizontally rotates a single wafer W whileit supports the single wafer W in the horizontal position when the spincleaning and spin drying treatments are applied thereto, and itcomprises a rotary shaft 10, a wafer supporting section 11 which isattached to and supported by the upper end portion of the rotary shaft10 in the horizontal position, and a driving motor 12 for rotatablydriving the rotary shaft 10.

The wafer supporting section 11 and the rotary shaft 10 are rotatablydisposed at the center of the cleaning housing 1 via a bearingsupporting cylinder 13 in a perpendicular position, and a single wafer Wcan be supported by the wafer supporting section 11 in the horizontalstate.

In particular, the wafer supporting section 11 is provided with a wafermounting section 14 for mounting and supporting the peripheral edge ofthe wafer W as shown in FIGS. 2 and 3.

The wafer mounting section 14 is supported horizontally by the wafersupporting section 11 and is composed of a cup body which is inclined atthe peripheral edge thereof and rises towards the outer region. Thewafer mounting section 14 has a plurality of claws 14 a, 14 a, etc. forsupporting the outer edge of the wafer W. The claws 14 a, 14 a, etc. ofthe wafer mounting section 14 are designed to have the same height, inorder that the peripheral edge of the wafer W can be supported in thehorizontal position. The supporting face of each claw 14 a has aconfiguration corresponding to the contour of the peripheral edge of thewafer W in cross section, and the peripheral edge corner section of eachclaw 14 a can contact and support the square peripheral edge of thewafer W in cross section in a point contact state or line contact state.

The rotary shaft 10 is rotatably supported by the bearing supportingcylinder 13 in the standing position, and the lower end portion of therotary shaft 10 is connected to the driving motor 12 so as to berotatably driven by the driving motor 12 via a belt entrainedtherebetween so that the wafer supporting section 11 is rotated at agiven speed of rotation. The speed of rotation of the rotary shaft 10 isset at low speed, e.g., 40–50 r.p.m. when the spin cleaning treatment iseffected while it is set at high speed of 3000 r.p.m. when the spindrying treatment is effected.

The cleaning chamber 3 is the section where the cleaning treatment isapplied to the wafer W, and the inner diameter dimensions thereof aredetermined in connection with the wafer supporting section 11 of thewafer rotary section 2, described hereinbelow, and has a cleaningtreatment space for the wafer W, which is rotatably supported by thewafer rotary section 2, at the outer region of the wafer rotary section2.

In detail, the cleaning chamber 3 has plural stages of annular treatmentbaths 15 to 18 which are arranged vertically at the inner peripherythereof as shown in FIGS. 1 and 2, and is constructed to move up anddown vertically relative to the wafer rotary section 2.

In the illustrated preferred embodiment, the four stages of annulartreatment baths 15 to 18 are arranged vertically and concentrically withthe wafer W so as to surround the wafer W which is supported by thewafer supporting section 11 of the wafer rotary section 2.

The peripheral inner edges of the annular treatment baths 15 to 18 arearranged in the manner that annular gaps defined between these edges areset to have small intervals to such extent for preventing the chemicalfluid(s) and the like from being leaked downward and at the same time donot contact the outer diameter edge of the wafer supporting section 11of the wafer rotary section 2.

The cleaning chamber 3 is constructed to be movable up and down, i.e.,vertically via an elevating guide (not shown), and has an elevatingmechanism 20 capable of elevating relative to the wafer supportingsection 11 of the wafer rotary section 2 by a given stroke.

The elevating mechanism 20 comprises a feed screw mechanism (not shown),which moves a supporting frame 21 for supporting the cleaning chamber 3up and down, and a driving motor 22 for rotatably driving the feed screwmechanism.

Depending on the cleaning treatment step, the cleaning chamber 3 ismoved up and down vertically by a given stroke via the feed screwmechanism when the driving motor 22 is driven while interlocking withthe operation of the wafer rotary section 2, described hereinbelow, sothat any one of the annular treatment baths 15 to 18 for effecting thecleaning treatment step may be selected from a position of heightrelative to the wafer W which is supported by the wafer supportingsection 11 of the wafer rotary section 2.

Drain sections, which communicate with the outside of the apparatus, arerespectively provided in the four annular treatment baths 15 to 18 (notillustrated in detail). These drain sections discharge the chemicalfluid(s) or the inert gas inside the annular treatment baths 15 to 18,in which they are structured to be opened only when the cleaningtreatment is effected and to be closed when the cleaning treatment iseffected in the other treatment baths.

The chemical fluid supply section 4 supplies the chemical fluid(s) tothe face of the wafer W which is rotatably supported by the wafer rotarysection 2, and it is provided on the upper portion of the cleaninghousing 1 and can communicate with the chemical fluid supply source 25provided outside the cleaning housing 1.

The chemical fluid supply section 4 is composed of injection nozzles forinjecting and supplying cleaning fluid(s) to the face of the wafer Wfrom above, which wafer W is rotatably supported by the wafer supportingsection 11 of the wafer rotary section 2. The chemical fluid supplysection 4 is structured so that it may be turned horizontally in adownward direction over the cleaning housing 1, and it is directlyconnected to a driving motor capable of being swung (not shown).

The chemical fluid supply section 4 is constructed to inject and supplythe cleaning fluid to the face of the wafer W which is rotatablysupported by the wafer supporting section 11 of the wafer rotary section2 in the horizontal position while the face of the wafer is turnedhorizontally from its outer peripheral portion toward the centerthereof.

In the illustrated preferred embodiment shown in FIGS. 1 to 5, thechemical fluid supply section 4 has nozzle ports each of which isidentified by a number corresponding to the kind of cleaning fluid(s) tobe supplied. In particular, three nozzle ports are provided (not shown)intended to serve as supply ports for an APM fluid, purified water and aDHF fluid

Injection nozzles 26 are opened at the upper end portion of the rotaryshaft 10 corresponding to the chemical fluid supply section 4, have thesame number of nozzle ports as those of the chemical fluid supplysection 4, i.e., three nozzle ports, and are constructed in such a wayas to inject and supply cleaning fluid to the back face of the wafer Wfrom the lower side. The injection nozzles 26 can communicate with thefluid supply source 25 via an internal pipe of the rotary shaft 10, andserve as supply ports for an APM fluid, purified water and a DHF fluid.

As a result, the wafer W can be cleaned at the front and back facesthereof at the same time or selectively.

The inert gas supply section 5 supplies the inert gas for preventingoxidation on the face of each wafer W which is rotatably supported bythe wafer rotary section 2 and can communicate with an inert gas supplysource 27 provided on the upper portion of the cleaning housing 1. Inthe illustrated preferred embodiment, a N₂ gas is used as the inert gas.

The inert gas supply section 5, as shown in FIG. 3 in detail, isprovided with a gas injection section 30 composed of a circular coverbody forming the drying sealed space A at the outer region of the faceof the wafer W which is rotatably supported by the wafer rotary section2 while cooperating with the cleaning chamber 3.

The outer periphery of the gas injection section 30, as shown in FIG. 3,is designed to engage with the inner peripheral portion of the cleaningchamber 3, namely, the outer periphery of the uppermost stage treatmentbath 18, whereby the sealed drying space A of necessary irreducibleminimum volume is formed at the outer peripheral portion of the face ofthe wafer W which is rotatably supported by the wafer rotary section 2.

The gas injection section 30 comprises a flat hollow body communicatingwith the inert gas supply source 27 via a communication pipe 33 at theinside thereof, and has a supply port 32 at its bottom portion as viewedfrom the above, namely, from the bottom plate 31 consisting of a flatplate.

The supply port 32 comprises a plurality of injection openings 32 a, 32a, etc. which are radially disposed and concentrically arranged with theface of the wafer W which is rotatably supported by the wafer rotarysection 2 (see FIG. 4), and structured in such a manner that the amountof N₂ gas supplied to the face of the wafer W at the outer peripheralportion of the wafer W is larger than that at the center thereof. Therationale for the construction of the supply port 32 is statedhereinbelow.

That is, the degree of oxidation on the wafer W depends on theconcentration of oxygen in the circum-ambient atmosphere on the face ofthe wafer W, and it has been found, as a result of research and testsconducted by the inventors, that concentration of oxygen on the face ofthe wafer W in the circum-ambient atmosphere thereof is higher at theouter peripheral portion of the face of the wafer W than that at thecenter thereof in an ordinary state as it directs toward the outerregion of the wafer W, as shown in FIG. 5.

It is therefore necessary to make the concentration of oxygen at theouter peripheral portion of the face of the wafer to become zero (0) orclose to zero (0) in order to prevent oxidation on the wafer W, and toattain this objective, the cleaning housing must be entirely purged bysupplying inert gas to the inside of the cleaning housing 1 which, aspreviously stated, requires a considerable volume of inert gas whichwould increase running costs and is therefore uneconomical.

Likewise, as already stated hereinabove, the amount of inert gassupplied to the face of the wafer must be such that the amount suppliedto the outer peripheral portion of the wafer is larger than that at thecenter thereof so that concentration of oxygen is substantially reducedto zero (0) or close to zero (0) while decreasing the usage of the inertgas as much as possible, thereby realizing the objective of preventingoxidation on the face of the wafer.

In order to concretely determine the amount of inert gas to be suppliedto the face of the wafer W, it has been proposed that the sum of theareas of these injection openings 32 a, 32 a, etc. at the outerperipheral portion of the wafer W is larger than that at the centerthereof and examples are shown in FIGS. 4(A), (B), (C) as the injectionopenings direct toward the outer peripheral portion of the wafer W.

That is, the injection openings 32 a, 32 a, etc. shown in FIG. 4(A) arecomposed of arc slits, and the length and width dimensions of such arcslits are determined to be larger at the outer peripheral portion of theface of the wafer W than those at the center thereof as the injectionopenings direct toward the outer peripheral portion of the wafer W.

Further, the injection openings 32 a, 32 a, etc. shown in FIG. 4(B) arecomposed of radially extended slits, and the width dimensions of suchslits at the outer peripheral portion of the face of the wafer W aredetermined to be larger than those at the center thereof as theinjection openings direct toward the outer peripheral portion of thewafer W.

Further, the injection openings 32 a, 32 a, etc. shown in FIG. 4(C)consist of circular openings which are arranged circumferentially andradially at prescribed intervals, and the diameter dimensions thereofare determined to be larger at the outer peripheral portion of the faceof the wafer W than those at the center thereof as the injectionopenings direct toward the outer peripheral portion of the wafer W.

Alternatively, although not shown, the number of disposition of theinjection openings 32 a, 32 a, etc. is determined to be larger at theouter peripheral portion of the face of the wafer W than that at thecenter thereof, or, the number of disposition of the injection openings32 a, 32 a, etc. may be combined with the construction of the areas ofopenings shown in FIGS. 4(A) to (C).

Although the amount of inert gas to be supplied can be controlled evenby merely setting the number of disposition or areas of openings of theinjection openings 32 a, 32 a, etc. according to the invention, a baffleplate 35 is interposed in the hollow section of the gas injectionsection 30 in addition to the construction set forth above.

The baffle plate 35 prevents the N₂ gas from directly flowing to thecenter of the supply port 32, and it consists of a discoid plate havinga diameter smaller than the bottom plate 31 of the gas injection section30.

The N₂ gas supplied to the inside of the gas injection section 30 viathe communication pipe 33 flows to an outer peripheral edge along theupper face of the baffle plate 35 and turns around the outer peripheraledge, then reaches the supply port 32 of the bottom plate 31 so that aconsiderable volume of N₂ gas can be supplied to the outer region of thesupply port 32.

Accordingly, the number of disposition and the areas of openings of theinjection openings 32 a, 32 a, etc. constituting the supply port 32 havebeen designed considering the operation of the baffle plate 35, therebyprescribing a flow rate model of the N₂ gas to achieve a zero (0)concentration of oxygen in the circum-ambient atmosphere on the face ofthe wafer W (see arrows in FIG. 2) while reducing the usage of N₂ gas asmuch as possible.

Further, the gas injection section 30 is movable up and down between ause position, where it cooperates with the cleaning chamber 3, i.e., theheight position shown in FIG. 3, and a use standby position, where thegas injection section 30 does not interfere with the chemical fluidsupply section 4, i.e., the height position shown in FIG. 1, anddrivably connected to an elevating means, not shown.

The fluid supply source 25 is intended to supply a chemical fluid forcleaning to the chemical fluid supply section 4, i.e., injection nozzles4 and 26, and has two chemical fluid systems, in the illustratedembodiment, by which the wafer W is to be cleaned with APM fluid(NH₄OH+H₂O₂+H₂O) or with DHF fluid (HF+H₂O). Annular treatment baths 15to 18 in the cleaning chamber 3 correspond to these two chemical fluidsystems, namely, the lowermost stage treatment bath 15 is used for thecleaning step by APM fluid, the third upper stage treatment bath 16 isused for the cleaning step by DHF fluid, the second upper stagetreatment bath 17 is used for the rinsing step by purified water, andthe uppermost stage treatment bath 18 is used for the spin drying step.

Under the single wafer type cleaning apparatus having the aforedescribedconstruction, when the cleaning chamber 3 is moved up and down, eitherthe wafer W supported by the wafer supporting section 11 of the waferrotary section 2 or the circular treatment baths 15 to 18 of thecleaning chamber 3 are selectively positioned, and the wafer W supportedby the wafer supporting section 11 is horizontally rotatable by thewafer rotary section 2 at a prescribed speed of rotation.

The chemical fluid supply source 27 is constructed to selectively effectcleaning steps of i) APM+DHF+(O₃+DIW)+DRY, ii) APM+DHF+DRY, iii)APM+DRY, DHF+DRY or the like, with the cooperation of the inert gassupply source 37, described hereinbelow, by appropriately selectivelysetting a recipe for cleaning steps.

The controller 6 controls the movement of these components of the singlewafer type cleaning apparatus while interlocking with these components,so that the following series of wet treatment steps are automaticallyeffected:

(1) The wafer W, before the cleaning treatment is applied thereto, isplaced in the wafer supporting section 11 inside the cleaning chamber 3via the wafer taking in/out port of the cleaning housing 1, (not shown),and when the cleaning chamber 3 is sealed, the wafer W is positioned atthe wafer cleaning treatment position inside the cleaning chamber 3 whenthe cleaning chamber 3 is moved up and down, and then various cleaningtreatments are effected in a predetermined procedure.

(2) For example, if the cleaning treatment is in the foregoing ii)cleaning treatment step (APM+DHF+DRY), the wafer W on the wafersupporting section 11 is positioned and disposed in the lowermost stagetreatment bath 15 when the cleansing chamber 3 is moved up and down insuch a way that the APM fluid is supplied from the injection nozzle 4,and a spin cleaning treatment is applied to the wafer W when the waferrotary section 2 is rotated at low speed.

(3) Subsequently, the wafer W is positioned and disposed in the secondupper stage treatment bath 17, and purified water is supplied from theinjection nozzle 4 and a rinsing treatment is applied to the wafer Wwhen the wafer rotary section 2 is rotated at low speed.

(4) Further, the wafer W is positioned and disposed in the third upperstage treatment bath 16, and the DHF fluid is supplied from theinjection nozzle 4 and a spin cleaning treatment is applied to the waferW when the wafer rotary section 2 is rotated at low speed.

(5) Further, the wafer W is positioned and disposed in the second upperstage treatment bath 17, and purified water is supplied from theinjection nozzle 4, and a rinsing treatment is applied to the wafer Wwhen the wafer rotary section 2 is rotated at low speed.

(6) Finally, the wafer W is positioned and disposed in the uppermoststage treatment bath 18, and a spin drying treatment is applied to thewafer W when the wafer rotary section 2 is rotated at high speed.

In the drying step, the gas injection section 30 of the inert gas supplysection 5 is lowered to a position shown in FIG. 3 to cooperate with thecleaning chamber 3 so as to form the sealed drying space A and then theN₂ gas is supplied to the sealed drying space A. The amount of N₂ gassupplied to the face of the wafer W is such that the amount of N₂ gassupplied to the outer peripheral portion of the face of the wafer W islarger than that at the center thereof.

Accordingly, when the inside of the sealed drying space A is cleaned bythe N₂ gas, or when occasion demands, air current is produced in thepassageway extending from the inert gas supply section 5 to the drainsection inside the sealed drying space A owing to the forceful dischargeof the N₂ from the drain section of the uppermost stage treatment bath18, concentration of oxygen at the entire outer region of the face ofthe wafer W is reduced to zero (0) or close to zero (0), when the spindrying treatment is applied to the wafer W.

(7) The wafer W is again taken out via the wafer taking in/out port ofthe cleaning housing 1 upon completion of a series of cleaningtreatments in the wafer cleaning apparatus.

Under the single wafer type cleaning apparatus constructed in theaforedescribed manner, the cleaning steps by the utilization of variouskinds of chemical fluids are effected relative to the face of the waferW in the sealed cleaning housing 1 in a predetermined order. Thereafter,the drying step proceeds through the spin drying treatment by which thewafer W is rotated at high speed by the wafer rotary section while an N₂gas is supplied to the face of the wafer W the wafer W, therebypreventing oxidation on the wafer W.

In this case, the N₂ gas supplied to the face of the wafer W is suchthat the amount of N₂ gas supplied to the outer peripheral portion ofthe face of the wafer W is larger than that at the center thereofthereby reducing the usage of the N₂ gas as much as possible to allowthe concentration of oxygen to become zero (0) or close to zero (0),thereby preventing oxidation on the face of the wafer W.

Although the foregoing embodiment is the preferred embodiment of theinvention, the invention is not limited thereto but can be designed andmodified in various ways within the scope of the invention.

For example, the wafer cleaning apparatus can be used as a singleapparatus, or as a basic construction element of a wafer cleaning systemprovided with a loading section, an unloading section or other types ofequipment such as placing and mounting robots and the like. Further, thechemical fluids employed by the preferred embodiment are merely samples,and hence other chemical fluids such as HPM (HCL+H₂O₂+H₂O), SPM(H₂SO₄+H₂O₂+H₂O) and the like can be used depending on the objectthereof.

1. A spin-drying method of wet-cleaned wafers which are not stored in a cassette, individually, in a sealed cleaning housing, said method consisting of the application of a spin drying treatment to the face of each wafer by supporting and rotating each wafer at high speed in the sealed cleaning housing while an inert gas for preventing oxidation is supplied to the face of the wafer in a drying step, where the inert gas is supplied to the inside of a gas injection section having a bottomplate and flows along the upper face of a baffle plate, turns around the outer peripheral edge of the baffle plate, and passes through injection openings of the bottom plate, said injection openings being located between the baffle plate and the wafer, where the amount of inert gas to be supplied to the face of each wafer is such that the amount of inert gas supplied at the outer peripheral portion is larger than that at the center thereof.
 2. The spin-drying method according to claim 1, wherein a sealed drying space is formed at the outer peripheral portion of the face of the wafer and the inert gas is supplied to the inside of the sealed drying space so that the space is filled with inert gas.
 3. The spin-drying method according to claim 1, wherein the inert gas employed is a nitrogen gas. 